Transcript Conduction and Convection

What’s so special about
convection, conduction, and
radiation?
Before we can start,
we need to be sure
we understand what
“transfer” means.
 Convection
 Conduction
 Radiation
–Are ALL ways of transferring heat

Heat always flows away from a hot material
toward a cold material
One picture is worth…..

In a solid material,
every atom is bonded
to a neighboring atom.

If we apply heat to one
part of a solid, like the
bottom of a metal pan,
the atoms begin to
vibrate.
Conduction
As the heated atoms
begin to vibrate more, the
bonds between the atoms
also begin to vibrate,
causing neighboring
atoms to collide.
 This passes the
vibrations, or heat, from
one atom to the next.
 Eventually, the energy
spreads throughout the
all the molecules of the
solid, and the
temperature increases.

So, (in words) what is conduction?

the direct transfer or movement of
warmth and energy from one molecule to
another molecule by collision.
What happens when you place a metal pot
or pan on a hot stove?
 Does the whole pan get hot, or only the
part touching the heat?

Most
solid metal materials transfer heat by conduction.
Conduction

This is why
when a metal
pot or pan is
placed on a hot
stove, the
whole pan
becomes hot,
rather than only
the bottom.
What are some other examples

Of conduction?????
Roasting marshmallows ……
Metal shed in sun……
Walking on sand ……
Convection

The Earth is heated by radiation from the
sun (transporting energy via electromagnetic waves).

Heating of earth's surface and atmosphere
by the sun drives convection within the
atmosphere and oceans, which produces
winds and ocean currents.

Convection is the transfer of heat by the
actual movement of warmed matter.
What’s happening
here?
Convection is typically demonstrated in liquids and gases and usually arises from
differences in temperature and density.
Where
is the
cooler
water?
Where
is the
warmer
water?
Examples of convection can be seen in the Earth’s
atmosphere and in the ocean currents.
Convection Currents
Air over the land is warm, cool air over water (ocean) rushes
in and pushes the warm air up – this is what causes the
wind to blow (convection currents)
Another way to see the same
thing….
In the atmosphere, as
air warms it rises, it
allows cooler air to
flow in underneath.
 This, along with the
turning of the Earth,
creates winds.

What causes
Convection currents to circulate?
 Lighter (less dense), warm material rises
while heavier (more dense) cooler
material sinks.
 This movement creates circulation
patterns known as convection currents in
the atmosphere, in water, and in the
mantle of Earth.
Convection Currents

This continual rising and
falling or air causes
breezes, winds, tornados,
and thunderstorms,
ocean currents, and also
causes the geologic
plates of the earth to
move.
Convection in the lava lamp
Convection in the lava lamp means that we also need to talk briefly about
density…..what is density?
Are cooler materials more or less dense than warm materials?
Can we pour air?
Is air a fluid?
Can we pour air?
Convection in the aquarium………
Heat causes warm water and molecules to
move faster and faster as they expand.
The cool water around the warm water
squeezes the warm water up.